Photometer.



A. ERHARDT.

PHOTOMETEB.

APPLIOATION 211.21) IDEO.16, 1911..

Patented May 21, 1912.

I UriITED ALBRECHT ERI-IABDT, 0F MUNICH, GERMANY.

PHOTOM'ETER.

Specification of Letters Patent.

Patented May 21, 1912.

Application filed December 15, 1911. Serial No. 665,961.

To all whom it may concern:

Be it known that I, ALBRECHT ERHARDT, a subject of theGerman Emperor, and residing at Munich, Germany, have invented certain new and useful Improvements in Photometers, of which the following is a specification.

The present invention has reference to improvements in devices for determining the proper exposure in photography, and it relates more particularly to a simple and reliable construction of exposure meter or photometer, by means of which the proper time for exposing the negative may directly be read off, without having to refer to special tables and to make more -or less troublesome computations as must now be done with most of the exposure meters known, such as for instance Wynnes Infallible or Heydes actino-photometer.

In order to make the invention more readily understood, I will now describe it with reference to the accompanying sheet of drawings, in which- I Figure 1 shows a front view of the stationary front plate; Fig. 2 shows a small, laterally reciprocated slide; Fig. 3 shows the large, vertically displaceable slide; Fig. 4 shows a front elevation of the stationary plate with the two slides in position relative thereto; Fig. 5 shows a side view of the device with thecasing in section; Fig. 6 represents a rear view, and Fig. 7 a top view of the device in natural size.

The stationary plate a is provided with two cut-outs a and the window a and contains above column-inscriptions referring to the character or brand of the plate or film -negative used, and in the center column inscriptions referring to the diaphragm or stop openings. In'the lower part is'provided a' slot a and below it two marks and the indications Light and Dark, for purposes to be hereinafter described.

The slide 0, by means of the handle 0 can be vertically reciprocated back of the plate a and is provided with a series of disks 0 of varying translucence, of graded colored glass or other suitable material. As shown, six such color disks are used, but their number, obviously, may vary from this. By shifting the slide, any one of these color disks may be made to register with the I terposed the laterally window a in the front plate a. At either side of the color disk column are tables denoting the various exposure periods in seconds and minutes and fractions thereof, which figures have been obtained by previous experiments,

Between the plate a and the slide a is indisplaceable slide 1), shown in Fig. 2, with two cut-outs b into one of which is fitted a plate 6 of a colored, translucent medium, preferably red glass, and these cut-outs are so disposed that in either end position of the slide 7) the window a is either unobstructed or in register with the colored plate 72 The slide bis provided below with a ledge 6 adapted to enga e, and slide in, the slot a in the front pate a, and a pointer Z2 tively to .one of the marks Light and Dark.

The described parts are preferably secured in a casing (Z, as shown in Fig. 5, provided rearwardly with an aperture e registering and with a viewing with the window a funnel or eye-piece 6. Obviously the plate a may also be so formed as to serve itself as casing.

The operation is the following :-The object to be photographed is to be viewed through the eye-piece c, with the two slides 71 and 0 in such position that the View through the window a is unobstructed,'and the pointer 77* points to the mark Light. The slide -0 is now shifted vertically by means of its handle until a colored disk 0 is interposed in front of the window a through which the object can just still be recognized. The test for the correct choice of disk is the fact that the succeeding darker on this ledge points respec disk will blot out the object. If all the disks to the sensitiveness of the negative employed, down to the horizontal line,

corresponding to the stop used. The square in which these two lines intersect contains the required exposure time. By way of example :-A. kodak film is used; the object to be photographed is very bright, consequently the slide Z) is shifted into the right-end position, its color plate 6 then lying back of the window a and the left table of exposure figures being exposed; the slide a is in its lowermostposition, its darkest color disk registering with the color plate 6 and the window a kodak. stop 32 is set. The required exposure will then be found to be 1/2 second. Without stop the exposure would be reduced to 1/50 second. Again, for a badly lighted object, the lowest color disk of greatest translucence has been determined on; the slide (2 is shifted to the lefthand position with its empty cutout back of the window a a normally rapid plate and continental stop 6, 8 are used then the correct exposure is shown to be 1/2 111il1- ute. TVith kodak stop 32, it would be 8 minutes. I

It will be noticed that the stop column in every square shows two dilferent figures, ex cept in the fourth division, the upper figure giving the stop as denoted on most continental cameras, and the lower figure that of kodak manufacture. The stop figure is identical in the two makes.

The figures 111, 90 and 7 8 on the plate a and the slide 0 denote the speed number of the plate or film.

It is obvious that the form of the device .may also be different, for instance oval or circular, instead of oblong as shown.

What I claim is 1. In aphotometer, the combination of a stationary 'front plate provided with platespeed indications and stopinscriptions and with a window, a slide providedwith columns of exposure figures, and with a plurality of disks of graded translucence, and means for vertically reciprocating said slide, whereby said disks are successively made to register with the window in said stationary plate, substantially as and for the purpose set forth.-

2. In a photometer, the combination of a stationary front plate provided with two sets of inscriptions denoting the character of the negative, with a stop column down the center, with a window and with two cut-outs flanking said stop column, a slide having two cut-outs, and a colored translucent plate in one such cut-out,means for laterally reciprocating said slide, and means for indicating its respective end positions, a second slide, a series of colored disks of graded translucence down the center of this second slide, two sets of vertically disposed col,- uinns of exposure figures thereon, and means for "ertically reciprocating said second slide back of said first slide, substantially as set forth.

In testimony whereof I alfix my signature in presence of two witnesses.

ALBRECHT ERHARDT. 

